I do have SIP disabled for DYLD_LIBRARY_PATH and a handful of other things, but macOS still says /usr/bin/command is on a read-only file system.
[edit]
Not hard to remount root as writable
$ sudo mount -uw /
Password:
$ sudo mv /usr/bin/command /usr/bin/command.save
$ tcsh
% command -v command
command: Command not found.
% command -V command
command: Command not found.
%
Now reversing the changes
% exit
exit
$ sudo mv /usr/bin/command.save /usr/bin/command
$ sudo mount -ur /
mount_apfs: volume could not be mounted: Invalid argument
mount: / failed with 66
Looks like I'll have to reboot to get the read-only state back.
